What does a faulty dmrv affect. How to check the air flow meter on your own and what do you need to check? Disassemble, clean, collect

The most obvious and early sign of a faulty or failing MAF is flickering lighting. dashboard. However, many malfunctions can cause this effect. Therefore, it is necessary to test the on-board computer of the car to make sure that this is due to the sensor. mass flow air.

Since the MAF plays an important role in maintaining the proper balance of air and fuel inside the engine, its failure can cause a range of performance problems. power unit. These may include low mileage after refueling, shaking when the engine is running, problems starting the engine, rattling or noises. These signs can appear much earlier than the DMRV reaches a critical state and the indicator on the dashboard lights up indicating a breakdown.

Sometimes the mass sensor air flow gets dirty and therefore starts to work poorly. Although the air passing through the MAF cleans it, microscopic debris accumulates on it. internal surfaces. Large accumulations of contaminants lead to damage to the device. In this case, the part can be returned to its original condition by simple cleaning. However, it is worth remembering that the sensor is a very delicate device and from careless handling it can become completely unusable.

There are other malfunctions of the DMRV. For example, if everything is in order with the device itself, the corrugated wire that connects it to the on-board computer may become unusable. As a result, the signal will be sent to the central processor with a delay, which will negatively affect the operation of the engine. To make sure that it works, you need to ring the wire or another similar device.

Diagnostics

The mechanic can check the on-board computer at service center. You can also do it yourself using a digital scanner for diagnosis. These scanners are available at most auto parts stores. While they all work a little differently, they are generally designed to connect to an OBD-II vehicle diagnostic port. Therefore, all scanners can read data from a computer.

After verification, the scanner will show one or more alphanumeric codes, which can be found in the directory. More advanced models display brief information about the code on the screen. If, after decryption, it becomes clear that the malfunction is related to the DMRV, then it must be replaced or repaired. It is worth noting that mass air flow sensors are rarely repairable, as they are easier and cheaper to simply replace.

To provide optimal process fuel combustion and compliance with the specified environmental standards, it is required to determine as accurately as possible the mass flow rate of air supplied to the engine cylinders, depending on the modes of its operation. This process can be controlled by a whole set of sensors: an air pressure sensor, a temperature sensor, but the most popular of them is a mass air flow sensor (MAF), which is sometimes also called a flow meter. The DMRV records the amount (mass) of air entering the engine intake manifold from the atmosphere and transmits this data to the electronic control unit for subsequent calculation of the fuel supply.

Types and features of flow meters

Deciphering the abbreviation DMRV - mass air flow sensor. The device is used in cars with gasoline and diesel engines. It is located in the intake system between the air filter and the throttle body and is connected to the engine ECU. In the absence or malfunction of the flow meter, the calculation of the amount of incoming air is carried out according to the position of the throttle valve. This does not give an accurate measurement, and fuel consumption increases in difficult operating conditions, since mass air flow is a key parameter for calculating the amount of fuel injected.

The principle of operation of the mass air flow sensor is based on temperature measurement air flow, and therefore this type of flowmeter is called hot-wire. Structurally, there are two main types of DMRV:

• nitium (wire);
• film;
• volumetric type with rotary damper (on this moment almost never used).

The design and principle of operation of the wire gauge

Nitievoy DMRV has the following device:

• frame;
• measuring tube;
• sensitive element - platinum wire;
• thermistor;
• voltage transformer.

The platinum filament and the thermistor are a resistive bridge. In the absence of air flow, the platinum filament is constantly heated to a predetermined temperature by passing through it. electric current. When the throttle valve opens and air begins to move, the sensor cools down, which reduces its resistance. This provokes an increase in the "heating" current to balance the bridge.

The converter converts the current changes that occur into an output voltage, which is transmitted to the engine ECU. The latter, based on the existing non-linear dependence, calculates the amount of fuel supplied to the combustion chambers.

This design has one significant disadvantage- Faults occur over time. The sensing element wears out and its accuracy drops. They can also get dirty, but to solve this problem, the wire-wound mass air flow sensors installed in modern cars have a self-cleaning mode. It involves short-term heating of the wire up to 1000°C with the engine off, which leads to the burning of accumulated contaminants.

Scheme and features of the film DMRV

The principle of operation of the film sensor is in many respects similar to the filament sensor. However, this design has several differences. Instead of a platinum wire, a silicon crystal is installed as the main sensitive element. The latter has a platinum coating, consisting of several the thinnest layers(films). Each of the layers is a separate resistor:

• heating;
• thermistors (two of them);
• air temperature sensor.

The sputtered crystal is placed in a case, which is connected to the air supply channel. It has a special design that allows you to measure the temperature of not only the incoming, but also the reflected flow. Since the suction of air is achieved by vacuum, the flow velocity is very high, which prevents the accumulation of contaminants on the sensing element.

Just as in a filament sensor, the sensitive element is heated to a predetermined temperature. When air passes through the thermistors, a temperature difference arises, on the basis of which the mass of the flow coming from the atmosphere is calculated. In such designs, the signal to the engine ECU can be supplied both in analog format (output voltage), and in a more modern and convenient for processing digital format.

Consequences and signs of a malfunction of the DMRV

As with any type of engine sensor, MAF malfunctions mean incorrect calculations by the engine ECU and, as a result, incorrect operation of the injection system. This can cause excessive fuel consumption or, conversely, insufficient supply, which reduces engine power.

The most striking symptoms of a sensor malfunction:

• The appearance of the "Check Engine" signal on the dashboard of the car.
• Significant increase in fuel consumption during normal operation.
• Reduced engine acceleration.
• Difficulties with starting the engine and the occurrence of spontaneous stops in its operation (the engine stalls).
• Work only at one certain speed level (low or high).

If you find signs of a malfunctioning mass air flow sensor, try disabling it. An increase in engine power will be a confirmation of the failure of the DMRV. In this case, it will need to be washed or replaced. In this case, it is necessary to select a sensor recommended by the car manufacturer (that is, the original one).

The mass air flow sensor (DMRV or flow meter) is important detail car, on the correct operation of which depends on the engine power and its fuel consumption. You can find it under the hood of the car, where it is located between the air filter and the air pipe directed to the throttle. The task of the DMRV is to measure the amount of air passing into the cylinders and transfer this information to the electronic control unit, that is, the “brains” of the machine. Based on the mass air flow sensor data, the control unit decides whether to increase or decrease the air supply to the combustible mixture.

In the event of a failure, the mass air flow sensor is almost never repaired, but simply replaced with a new one. Its device is quite simple, and it consists of a housing in which a device for measuring air consumption is placed - a hot-wire anemometer. It is enough to damage the diagnostic device in the process of dismantling the MAF or cleaning it, and the entire sensor will need to be replaced. It can also fail with a long service life, but you can only verify its malfunction after checking.

Symptoms of a malfunctioning mass air flow sensor

Before proceeding with the check of the DMRV, it is necessary to understand from the primary symptoms that it is faulty. The following symptoms may indicate problems with the sensor:

The above symptoms indicate that the air is not supplied to the combustible mixture in the volume in which it is necessary. Moreover, this problem can be observed not only when the DMRV fails. In particular cases, the malfunction may be due to the lack of power to the sensor through the wiring or cracks in the connecting hoses.

How to check the DMRV for serviceability

There are several basic methods for checking the mass air flow sensor, which allow you to verify that it is malfunctioning.

Checking the DMRV in motion

The easiest way to diagnose the flow meter is to analyze the operation of the engine when the sensor is forced off. The check goes like this:

Checking the MAF with a multimeter

You can diagnose a problem with the sensor using a multimeter. To do this, you must first deal with the design of the device and its "pinout", that is, the wiring of the wires on the board. There are 4 wires coming out of the mass air flow sensor. Depending on the DMRV model and manufacturer, their colors may vary, but in most cases they are as follows:

• Pink (or pink-black): wire to the main relay;
• Green: wire to ground;
• Gray: wire to power;
• Yellow: signal input.

To test the mass air flow sensor, the multimeter must be set to DC voltage measurement mode and set to a limit of 2 volts. Next, you need to turn on the ignition, but do not start the engine. When this is done, connect the multimeter's red lead to the sensor's signal input ( yellow wire), and the black probe to ground (green wire). This can be done without "exposing" the wires by inserting the probes of the diagnostic device through rubber compressor connector.

Based on the measurement results, we can draw conclusions about the state of the sensor:

Some modern on-board computers allow you to watch the voltage on the mass air flow sensor. In such situations, you can do without a multimeter.

Visual inspection of the DMRV

Experienced motorists can determine the malfunction of the mass air flow sensor by its appearance. The first step is to remove the DMRV, and then carefully examine it. Signs of a malfunction are the ingress of liquid into the air pipe and the DMRV sensor (or the presence of mechanical damage).

Most often, liquid can end up in the sensor for the following reasons:

• Increased oil level in the crankcase. In such a situation, oil enters the sensor;
• Clogged oil separator of the crankcase ventilation system;
• Untimely replacement of the air filter, due to which dirt gets on the hot-film DMRV.

The easiest and most reliable way to diagnose problems with the mass air flow sensor is to replace it with a working device. For example, you can remove a suitable working sensor from another vehicle, install it and check that the engine has stabilized. In such a situation, you can immediately go to buy a new sensor without diagnosing it with a multimeter or in other ways.

Air Flow Sensors

The air flow sensor is used to measure the amount (volume or mass) of air consumed by the engine. The value of the mass of incoming air, measured directly by the mass air flow sensor or calculated by the engine control unit from its volume, is one of the basic parameters in determining the duration of opening. The air flow sensor is installed after the air filter before the throttle valve. On the side of the inlet part of the air flow sensor housing, there is a grid or laminating honeycombs that equalize the air flow over the entire area of ​​the air meter.

Exist various designs air flow sensors, but each of them can be attributed to one of two types - volumetric air flow sensors, and mass air flow sensors. Mass air flow sensors (MAF) are more preferable, as they directly measure the mass air flow (MAF takes into account temperature and pressure atmospheric air), due to which the engine control unit can more accurately calculate required amount injected fuel.
In addition, the design of the mass air flow sensor (MAF) has no moving mechanical parts. But due to the complexity of the mass air flow sensors, early engine control systems used mainly volume air flow sensors. Volumetric air flow sensors are less preferred as they only measure the volume of air flowing. And the mass of air (as well as any other gases), filling, for example, a volume equal to one liter, depends very much on its pressure and temperature.

The engine control unit calculates the mass air flow, additionally taking into account atmospheric pressure and the readings of the air temperature sensor in the intake tract. Each of these sensors has its own error, as a result of which the calculated value of the mass air flow may differ slightly from the actual flow. The engine control unit calculates from the value of the mass of air entering the engine into the value of the mass of fuel required for each cylinder. It should be noted that all air flow meters determine the continuous flow rate, and the fuel is injected by injectors in portions, synchronously with the cycles of the cylinders.
The output signal of the air flow sensor can be analog or digital. In the first case, depending on the air flow, the voltage of the sensor output signal changes, in the second case, the frequency or duty cycle of the sensor output signal changes. For example, the output signal of some mass air flow sensors manufactured by GM, MITSUBISHI is a frequency-varying square-wave voltage. As the air flow through the sensor increases, the frequency of the output signal increases.

Air flow sensor

Most air flow sensors work according to one of two principles: either the Karman vortex counting principle is used (some sensors manufactured by MITSUBISHI, CHRISLER ...), or the principle of shifting the potentiometer slider using a blade placed in the air flow consumed by the engine. Air flow sensors based on the Kármán vortex counting principle have high reliability because they have no moving mechanical parts.

Volumetric air flow sensor based on the principle of Karman vortex counting.

Volumetric air flow sensor, with mechanical measuring potentiometer.

BOSCH potentiometric air flow sensor.
Volumetric air flow sensors operating on the principle of shifting the potentiometer slider with the help of a measuring blade have low reliability, since their design includes moving mechanical elements. The blade of such a sensor is spring-loaded and placed in the flow of air consumed by the engine so that with an increase in air flow, the blade shifts in proportion to the flow. The flow of air consumed by the engine has a pulsating character, and in order to reduce the effect of pulsations of the measuring blade synchronously with the pulsations of the air flow, the sensor blade is connected to a damper. A potentiometer slider is mechanically connected to the measuring vane, which due to this is shifted by an amount proportional to the amount of air flow. The measure of the volume of air flowing through the sensor is the output voltage of this measuring potentiometer. The measuring potentiometer of the volumetric air flow sensor is made on a ceramic substrate. The voltage divider resistors are deposited on the substrate, the leads of which are placed in a row and covered with a contact resistive layer. The slider of the potentiometer is pressed against the contact resistive layer, due to which the voltage on the slider is equal to the voltage at the point of contact with the resistive layer.

BOSCH volumetric air flow sensor potentiometer.
With each change in the position of the blade, the slider moves along the contact resistive layer, sliding over it. Such movements of the slider gradually abrade the contact resistive layer, which over time leads to the appearance of "wear" of the measuring potentiometer. When the slider enters the “wear” zone, where the contact resistive layer is worn down to the ceramic substrate, the electrical contact between the slider and the resistive layer deteriorates, as a result of which the output voltage of the potentiometer no longer corresponds to the position of the movable blade of the flowmeter - that is, the output voltage of the sensor does not correspond to the value air consumed by the engine. Typical malfunction volumetric air flow sensors operating on the principle of displacement of the potentiometer slider, is the mechanical wear of the resistive layer. Wedging of the sensor blade is also common. The reasons for the wedging of the blade may be wear of the blade supports, deformation (curvature) of the blade due to strong pops in the intake manifold or due to contamination of the air channels of the sensor. The method for diagnosing a volumetric air flow sensor operating on the principle of potentiometer slider displacement is similar to the method for diagnosing a potentiometric throttle position sensor (or any other potentiometric position sensor).

Mass Air Flow Sensor (MAF Sensor)

The measuring element of the mass air flow sensor is a wire or film element heated to a certain predetermined temperature. The flowing air stream cools this element, but circuit diagram(usually built into the flow meter) controls the power of its heating and heats the measuring element to its previous temperature. The more air flows through the flow meter, the more heating power is required to maintain the set temperature of the measuring element. Thus, the heating power of the measuring element of the flow meter is a measure of the amount of air flowing through the sensor. The value of the heating current of the measuring element is converted into the output signal of the sensor - in most cases, into an analog voltage, in some types of flowmeters into a rectangular voltage with a variable frequency.

BOSCH HFM5 Mass Air Flow Sensor

There are several designs of mass air flow sensors, but in last years BOSCH's HFM 5 mass air flow sensor has become widespread.

Mass air flow sensor BOSCH HFM5.
The output signal of the mass air flow sensor BOSCH HFM5 is a DC voltage that varies in the range of 0...5V. The output signal voltage of the sensor depends on the magnitude and direction of the air flow passing through the sensor. At zero air flow (engine stopped, ignition on), the output voltage of the mass air flow sensor is 1.00V. When the engine is running, air flows through the sensor, and the more air flow, the higher the output voltage value of the sensor. At certain engine operating modes, short-term reverse air flows may occur - when air moves in the direction from the engine intake manifold to air filter. The BOSCH HFM5 mass air flow sensor is capable of detecting reverse air flows, while its output voltage is reduced to values ​​less than 1.00 V in proportion to the amount of reverse flow. If the signal from the mass air flow sensor deviates from the norm, the engine performance deteriorates significantly - fuel consumption increases, the engine "acceleration" decreases, the engine operation becomes unstable in established modes, and a difficult cold start of the engine appears. Deviations in the parameters of the output signal can be associated with the "deterioration" of the characteristics of the mass air flow sensor, the suction of "unaccounted" air into the intake tract, and the instability of the sensor supply voltage. In case of contamination on the measuring element of the sensor, the reaction speed of the sensor to changes in the air flow decreases, as well as the measurement accuracy decreases, which, as a result, leads to the preparation of an air-fuel mixture with wrong composition. Intensive deposition of dirt on the sensitive element of the sensor may occur due to untimely replacement of the air filter. Sometimes damage to the sensor is observed when the output signal is constantly within 1.00V and does not change with increasing air flow. The engine starts normally, but immediately stalls. In most cases, the engine control unit can only fully determine faulty flow meter. "Deterioration" of the sensor's characteristics is determined by the control unit in rare cases.

BOSCH HFM5 Sensor Output Check

To view the voltage waveform of the output signal of the BOSCH HFM5 mass air flow sensor, it is recommended to use a differential oscilloscope probe. The differential oscilloscope probe connector must be connected to the USB Autoscope II differential analog input #6. The black alligator clip of the differential oscilloscope probe must be connected to the engine ground of the vehicle being diagnosed. The negative probe of the probe (black) must be connected in parallel with the "signal ground" of the sensor (terminal No. 3 of the sensor connector), the positive probe of the probe (red) must be connected in parallel with the signal output of the sensor (terminal No. 5 of the sensor connector).

Scheme of connection to the BOSCH HFM5 mass air flow sensor.

1. connection point of the black alligator clip of the differential oscilloscope probe;


2. negative probe connection pointdifferentialoscilloscope probe (black);


3. positive probe connection pointdifferentialoscilloscope probe (red).

Measurement of transient time at power-up.

At the moment the ignition is turned on, supply voltage is applied to the sensors and actuators of the engine control system, including the air flow sensor. Immediately after power is applied to the BOSCH HFM5 mass air flow sensor, its sensing element heats up to operating temperature, at the same time, while the temperature of the sensor stabilizes, a transient occurs.

Oscillogram of the output voltage of a working BOSCH HFM5 mass air flow sensor when supply voltage is applied.
A: (engine stopped) and equal to 0.99 V;
ATpower supply to the sensor and is equal to ~0.5 mS.
The transient time of the output signal of a healthy sensor does not exceed a few milliseconds (mS). Contaminants deposited on the sensitive element of the sensor are heated along with it. If the amount of deposited contaminants is significant, the heating time of its sensitive element to the operating temperature increases, and accordingly, the duration of the transient process also increases.

Oscillogram of the output voltage of a defective BOSCH HFM5 mass air flow sensor when supply voltage is applied.
A: voltage value at the moment of time indicated by the marker. In this casecorresponds to the output signal voltage of the MAF at zero air flow(engine stopped) and equal to 0.92V;
AT the value of the time interval between two markers. In this casecorresponds to the transient time of the output signal when applyingpower supply to the sensor and is equal to ~ 70mS.
The transition time of the output signal of a sensor with a contaminated measuring element can reach tens and sometimes hundreds of milliseconds.

Output voltage measurement at zero air flow.

Measurement of the voltage value of the output signal of the sensor at zero air flow is carried out with the engine stopped and the ignition on. For the BOSCH HFM5 mass air flow sensor, zero air flow corresponds to an output voltage value of 1V ± 0.02 V.

Measurement of the output voltage during a sharp overgassing.

Measurement of the maximum value of the voltage of the sensor output signal during a sharp overgas is carried out by a sharp opening of the throttle valve on a short time(no more than one second) provided that the transmission mode switch is in the "Neutral" position and the engine is warmed up to operating temperature. Attention. The method for measuring the maximum voltage value of the output signal of the air flow sensor during a sharp overgas is applicable only if the accelerator pedal of the diagnosed engine is mechanically connected to the throttle valve (using a cable / levers) and only for atmospheric engines (the diagnosed engine is not equipped with a turbine / compressor) . At the moment of sharp regassing, the following occurs. When the engine is running at idle without load, the air filling the intake manifold is very rarefied, since the air flow into the intake manifold is limited by the throttle valve and the idle valve. The absolute pressure in the intake manifold is lower than atmospheric by 0.6 ... 0.7 Bar. The mass of rarefied air filling the manifold is negligible. With a sharp opening of the throttle, air rushes sharply through the open throttle into the intake manifold and quickly fills the volume of the manifold until the absolute pressure in it reaches a value close to atmospheric. This process occurs very quickly, as a result of which the air flow through the air flow sensor reaches values ​​close to the maximum. After the absolute pressure in the intake manifold reaches close to atmospheric pressure, the amount of air flowing through the sensor becomes proportional to the engine speed.

Oscillogram of the output signal voltage of a serviceable BOSCH HFM5 during a sharp overdrive. The voltage of the output signal of a healthy BOSCH HFM5 mass air flow sensor immediately after a sharp opening of the throttle should briefly increase to a value of at least 4.0V. In case of significant contamination of the sensitive element of the sensor, the reaction speed of the sensor decreases, and the shape of the sensor output voltage waveform becomes somewhat "smoothed". Contaminants deposited on the sensitive element of the sensor form a heat insulator that reduces the intensity of cooling of the sensitive element of the sensor, which leads to a decrease in the heating current and the output signal of the sensor (accordingly, the amount of fuel supplied to the cylinders also decreases).

Oscillogram of the output signal voltage of a faulty BOSCH HFM5 mass air flow sensor during a sharp overgas.
Due to the reduced response speed, the sensor's ability to detect rapid changes in the magnitude and direction of the airflow is degraded. As a result, after a sharp opening of the throttle, the voltage of the output signal of such a sensor no longer has time to reach the value of 4.0V. Sensor malfunctionsBOSCH HFM5 Air Mass Eliminatedjust by replacing it.

A car engine has many modes of operation and each of them requires a combustible mixture of the correct consistency, in other words, the ideal ratio of air and fuel. This is exactly what the mass air flow sensor (DMRV, flow meter, MAF - Mass Airflow) monitors.

The main task of the flow meter is to determine the amount of air that enters the cylinders and transmit this information to the computer, which already draws the appropriate conclusions and decides to increase or reduce the amount of air or fuel. DMRV consists of: plastic case and hot-wire anemometer, which measures air consumption.

Violations in the operation of the mass air flow sensor are fraught with interruptions in the operation of everything. It is very easy to damage or disable the flow meter, it will be enough to use excessive force when cleaning or dismantling the mass air flow sensor. At the same time, this sensor cannot be repaired; the malfunction can only be eliminated by completely replacing it.

Signs of a malfunctioning DMRV:

1. Rough operation of the engine at idle.
2. Deterioration of acceleration dynamics - "dumb acceleration".
3. Too high or low idle.
4. Increased fuel consumption.
5. The engine does not start.

However, one cannot exclude other reasons why the DMRV may not work. For example, if the hose connecting the flow meter and throttle module is cracked, the sensor wiring is damaged, or there are other power problems mass air flow sensor, may look defective.

How to check the DMRV?

Method One - disable the sensor

Disconnect the sensor connector, then try to start the engine. When the DMRV is turned off, the controller starts to work in emergency mode, and the fuel-air mixture is prepared taking into account the throttle position, which is reported by another equally important sensor called TPS (). The engine speed should be around 1500 rpm. Get behind the wheel and try to drive, if during acceleration you feel that the car "came to life" and the dynamics improved noticeably, we conclude - faulty DMRV.

Method Two - ECU firmware

If you have replaced the standard ECU firmware with another one (with different settings), try this: slip a thin plate 1 mm thick under the damper stop. As a result, your speed should rise, then remove the chip from the DMRV. If the motor continues to run and does not stall, most likely the reason lies in the firmware.